alkanes

• alkanes = homologous series of saturated hydrocarbons
• bonding

  • single covalent bonds
  • sigma bonds
  • free rotation
  • tetrahedral shape - 109.5
• properties

  • non polar molecules
  • induced dipole - dipole interactions (london forces)
  • boiling point increases down the group
  • boiling point decreases with more branching as there are less points of contact
• reaction of alkanes - combustion

  • very low reactivity due to sigma bonds having low polarity and high bond enthalpy
  • exothermic
  • complete combustion = water and carbon dioxide produced
  • incomplete combustion = water and carbon monoxide or soot produced
• reaction of alkanes - free radical substitution

  • initiation = diatomic halogen molecules can be evenly split into halogen radials via homolytic fission by UV radiation
  • propagation (2 steps) = halogen radial removes a hydrogen from alkane forming an alkyl radical and then the alkyl radical removes a halogen forming a halogen radical again
  • termination = 2 radicals react together to form a covalent bond